1. Field of the Invention
The present invention relates to a zoom lens unit and an imaging apparatus including the zoom lens unit. In particular, the zoom lens unit according to the present invention is suitable for use in such as a video camera or an electronic still camera which employs a solid-state image sensor as an imaging device. The imaging apparatus including the zoom lens unit according to the present invention is suitable for use as a video camera or an electronic still camera.
2. Description of the Related Art
In recent years, higher performance and compactness have been required for digital cameras. In addition, both higher performance and compactness have been required for zoom lens units used in photographing lenses. Considering the application of the zoom lens unit to a high end, for example, the digital camera, at least a resolution corresponding to an image pickup device having 5 million to 10 million pixels over all a zoom area is necessary to achieve higher performance of such zoom lens units.
In addition, many users require a photographing lens with wide-angle capability and high magnification ratio, and it is desirable that a half-field angle of a zoom lens unit at a wide-angle end be 38 degrees or more. The half-field angle of 38 degrees corresponds to a focal length of 28 mm in terms of a 35 mm silver salt camera (so-called Leica version). Moreover, a magnification ratio of five or more is desired.
Regarding compact cameras, JP H8-248318 A and JP 2005-215165 A disclose zoom lens units in which a prism is disposed in an optical system to bend the light path, and thus a thin-model camera equipped with the zoom lens unit can be obtained.
Each zoom lens unit described in JP H8-248318 A and JP 2005-215165 A is suitable for a video camera, and a magnification ratio is 8 times or more in an embodiment of JP H8-248318 A, or is 7 times or more in an embodiment of JP 2005-215165 A, both of which are excellent. However, a half-field angle at a wide-angle end is about 33 degrees in JP H8-248318 A, or is about 34 degrees in JP 2005-215165 A, therefore both fail to achieve a half-field angle of 38 degrees or more, which is desirable for digital cameras recently.